<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        ul {
            list-style: none;
        }

        .box {
            /* display: none; */
            width: 200px;
            height: 200px;
            background-color: orange;
            transition: all ease .8s;
            /* visibility: hidden; */
            opacity: 0;
        }

        body:hover .box{
            /* display: block; */
            width: 400px;
            height: 400px;
            /* visibility: visible; */
            opacity: 1;
        }
        /* 过渡 和  display  有冲突 */
    </style>
</head>

<body>
    <div class="box">

    </div>
</body>

</html>